Pipe systems are used in industrial environments, for example food industry or oil industry, for transporting contents like raw materials, half products or end products to various stages in corresponding processes. Such pipe systems need periodic cleaning and therefore the pipe system contents, i.e. the product need to be cleared from the pipe system. After clearing the pipe system, cleaning can be performed. Such cleaning is in the art also referred to as ‘Cleaning In Place’ (CIP).
While clearing the pipe system, the cleared contents are preferably preserved for later use or recycling in the process in which the pipe system is used. For this reason is it advantageous to clear the pipe before cleaning by pushing out the pipe system contents using a air. Usually compressed air is used, but dependent on the contents, other gasses may be applicable.
In the art it is known that clearing a pipe system can be performed by blowing out the pipe system contents in a push phase, wherein high pressure air is applied at a pipe system proximal end such that the pipe contents are set in motion. When most of the contents are cleared from the pipe system, a constant air flow in a blow phase will remove the remaining contents which adhered to the pipe system walls, after which the pipe system can be rinsed and dried in respective rinse and dry phases.
Clearing the pipe system in the push phase requires adequate pressure and speed. When the pressure is too low, the air used for expelling the contents tends to flow over the pipe system contents and find its way to an distal end. Thereby contents are left inside the pipe system.
When the pressure is too high, the air can push through the pipe contents, creating so called ‘rat holes’ i.e. passages through the contents.
Adequate initial pressure and pressure profile in time of the compressed air in the push phase can determined from contents viscosity, pipe diameter and architecture, and can also be determined from experience. The air pressure profile in time and consequential flow, once the air is released in the push phase, also determines adequate expelling of the pipe system contents.
In the art, a predetermined air pressure profile is released upon the pipe system contents, starting at an initial pressure, decreasing to an end pressure. The push phase is ended when the end pressure is reached, i.e. the pressure drops below a threshold value, or when the push phase is timed out. In these cases the pressures and pressure profiles are chosen such that at the end of the push phase a sufficient normalized amount of the contents has been cleared. In other cases the push phase is ended when a sudden unexpected pressure drop is detected. In the latter case, the pipe system contents were completely expelled prematurely.
When an insufficient normalized amount of contents have been cleared, or when the push phase end prematurely relatively large normalized amounts of contents remain in the pipe system. Consequently an extensive blow phase is required to eventually clear the pipe system of its contents.
When too much contents are cleared from the pipe system in the push phase, compressed air may undesirably enter a container used for capturing contents removed from the pipe system, i.e. product, thereby causing overpressure in such a container and consequently obstructing filling of the container.
As a pipe system may comprise many product feed line or pipes, each of which have to be cleared during production, and wherein pipes are made from opaque materials such as stainless steel, it is not possible to follow the pipe content while it is being cleared from the pipe. Thus completion of the clearing of the pipe system is uncertain.